Vehicle communication system and vehicle-mounted device

1. A vehicle communication system comprising: a vehicle-mounted device having a microcomputer that transmits signals from a plurality of transmitting antennas provided on a vehicle, the plurality of transmitting antennas including: a first transmitting antenna provided in a vehicle cabin nearer to a first side surface in a width direction of the vehicle from a central portion, and a second transmitting antenna provided nearer to a second side surface in the width direction of the vehicle; and a mobile device that receives the signals transmitted from the vehicle-mounted device and transmits a response signal including received signal strengths of the received signals, in which the vehicle-mounted device receives the response signal transmitted from the mobile device and determines whether the mobile device is present inside the vehicle cabin or not based on the received signal strengths included in the received response signal, wherein the microcomputer is configured to: determine whether or not the mobile device is present inside an area containing a vehicle interior space and having a boundary surface following at least the first side surface in the width direction of the vehicle, based on the received signal strengths of the signals transmitted from the first transmitting antenna and the second transmitting antenna, respectively, adding the received signal strength of the signal transmitted from the second transmitting antenna to the received signal strength of the signal transmitted from the first transmitting antenna, and determine whether the mobile device is present inside the area based on a value obtained by adding the received signal strength of the signal transmitted from the second transmitting antenna to the received signal strength of the signal transmitted from the first transmitting antenna, such that a concave of an other side surface of the area in the width direction of the vehicle is corrected without distortion of the boundary surface of the area following one side surface in the width direction of the vehicle.

2. The vehicle communication system according to claim 1 , wherein the microcomputer multiplies the received signal strength of the signal transmitted from the second transmitting antenna, by a weight coefficient that is less than one, and adds the weighted received signal strength to the received signal strength of the signal transmitted from the first transmitting antenna.

3. The vehicle communication system according to claim 1 , wherein the plurality of transmitting antennas include a third transmitting antenna provided in the vehicle cabin, the microcomputer determines a third value by adding the received signal strength of a signal transmitted from the second transmitting antenna to a received signal strength of a signal transmitted from the first transmitting antenna, the microcomputer determines a fourth value by adding the received signal strength of the signal transmitted from the second transmitting antenna to a received signal strength of a signal transmitted from the third transmitting antenna, and the microcomputer determines whether the third and fourth values satisfy a predetermined determination expression or not.

4. The vehicle communication system according to claim 3 , wherein the microcomputer is configured to: multiply the received signal strength of the signal transmitted from the second transmitting antenna by a first weight coefficient that is less than one, and add a weighted received signal strength to the received signal strength of the signal transmitted from the first transmitting antenna, and multiply the received signal strength of the signal transmitted from the second transmitting antenna by a second weight coefficient that is less than one, and add a weighted received signal strength to the received signal strength of the signal transmitted from the third transmitting antenna.

5. The vehicle communication system according to claim 1 , wherein the plurality of transmitting antennas include a third transmitting antenna provided in the vehicle cabin, the microcomputer calculates a scalar determination value for determining whether the mobile device is present inside the area or not, based on the received signal strengths of the signals transmitted from the first transmitting antenna, the second transmitting antenna and the third transmitting antenna, respectively, and the microcomputer compares the calculated scalar determination value with a predetermined threshold value.

6. The vehicle communication system according to claim 1 , wherein the area includes an entirety of the vehicle interior space and part of the outside of the vehicle and having a boundary surface following the first side surface in the width direction of the vehicle.

7. A vehicle-mounted device that transmits signals from a plurality of transmitting antennas provided on a vehicle to a mobile device and determines whether the mobile device is present inside a vehicle cabin or not based on received signal strengths of the signals received by the mobile device, the plurality of transmitting antennas including: (i) a first transmitting antenna provided in a vehicle cabin nearer to a first side surface in a width direction of the vehicle from a central portion, and (ii) a second transmitting antenna provided nearer to a second side surface in the width direction of the vehicle, the vehicle-mounted device comprising: a microcomputer configured to: determine whether or not the mobile device is present inside an area containing a vehicle interior space and having a boundary surface following at least the first side surface in the width direction of the vehicle, based on the received signal strengths of the signals transmitted from the first transmitting antenna and the second transmitting antenna, respectively, add the received signal strength of the signal transmitted from the second transmitting antenna to the received signal strength of the signal transmitted from the first transmitting antenna, and determine whether the mobile device is present inside the area based on a value obtained by adding the received signal strength of the signal transmitted from the second transmitting antenna to the received signal strength of the signal transmitted from the first transmitting antenna, such that a concave of an other side surface of the area in the width direction of the vehicle is corrected without distortion of the boundary surface of the area following one side surface in the width direction of the vehicle.